1. Field of the Invention
The present invention relates to an optical equipment, such as camera, equipped with a device for detecting the visual axis of the observer, observing an object through a view finder system of said equipment, utilizing a reflected image of the eyeball of said observer, obtained by illuminating said eyeball.
2. Related Background Art
There are already proposed various devices, such as eyeball camera, for detecting so-called visual axis of the observer, or detecting the position of observation of the observer within a plane to be observed. The method for detecting said visual axis, disclosed for example in the Japanese Patent Application Laid-open No. 1-274736 consists of projecting a light beam from a light source onto a front portion of the eyeball of the observer, and determining the visual axis by a reflected corneal image formed by the light reflected from the cornea and the focal position of the pupil.
FIG. 46 shows the basic principle of detecting the visual axis, wherein light source 13a, 13b, such as light-emitting diodes, emitting infrared light not visible to the observer, are positioned substantially symmetrically in the X-direction with respect to the optical axis of a light-receiving lens 12 and illuminate the eyeball of the observer with diverging light beams. A part of the illuminating light reflected by the eyeball is concentrated by the lens 12 onto an image sensor 14. FIG. 47A is a schematic view of the image of the eyeball projected on said image sensor 14, and FIG. 47B is a chart of the output intensity of said image sensor 14. The method of detection of visual axis will be explained in the following, with reference to these drawings.
The infrared light emitted from the light source 13b illuminates the cornea 16 of the eyeball 15 of the observer, and a reflected corneal image P1 (false image) formed by a part of the infrared light reflected on the surface of the cornea 16 is concentrated by the light-receiving lens 12 and is focused at a position Xp1 on the image sensor 14. Similarly the infrared light emitted from the light source 13a illuminates the cornea 16, and a reflected corneal image P2 formed by a part of the reflected infrared light is focused by the lens 12 onto a position Xp2 of the image sensor 14.
Also the light beams from end portions a, b of the iris 17 are guided through said lens 12 to form the images of said end portions a, b at positions Xa, Xb on the image sensor 14. If the rotation angle .theta. of the optical axis of the eyeball 15 is small with respect to the optical axis of the light-receiving lens 12, the coordinate Xc of the center c of the pupil 19 is represented as: EQU Xic.perspectiveto.(Xa+Xb)/2.
Also since the coordinate x of the middle point of the corneal reflected images P1 and P2 substantially coincides with the x-coordinate x.sub.o of the center O of curvature of the cornea 16, the rotation angle .theta..sub.x of the otpical axis of the eyeball 15 in the Z-X plane substantially satisfies a relation: EQU .beta.*OC*SIN.theta.X.perspectiveto.(Xp1+Xp2)/2--Xic (1)
wherein OC is a standard distance between the center O of curvature of the cornea 16 and the center C of the pupil 19. .beta. is a magnification determined by the position of the eyeball with respect to the lens 12 and is practically determined as a function of the distance .vertline.Xp1-Xp2.vertline. of the corneal reflected images, and * indicates multiplication.
These drawings illustrate the calculation of the rotation angle .theta.x in case the eyeball of the observer rotates in the Z-X plane (for example horizontal plane), but the rotation angle .theta.y in case of rotation in the Y-Z plane (for example vertical plane) can be calculated in a similar manner.
With such calculations of the rotation angles .theta.x, .theta.y of the optical axis of the eyeball of the observer, the position (X, Y) observed by the observer for example on a focal screen in a single lens reflex camera can be represented as: EQU X=m**(Ax*.theta.x+BX) (2) EQU Y=m*(Ay*.theta.y+By) (3)
wherein m is a constant, determined by the view finder system of the camera and used for converting the rotation angle into the coordinate on the focal screen. Also Ax, Ay, Bx, By are visual axis correcting coefficients for correcting the individual difference in the visual axis of the observer, and can be determined from the rotation angles of the eyeball obtained at observing two different targets.
Also the method of detecting the visual axis when the camera is in a vertically oblong position is already proposed, for example, in the Japanese Laid-Open Patent Application No. 3-107909. FIG. 48 is a partial schematic view (in the vicinity of the eyepiece lens of the view finder system) of an optical equipment provided with a visual axis detecting device proposed in said patent application.
As shown in this drawing, the light sources 13a, 13b are turned on in the normal camera position, and the light sources 13b, 13c are turned on in the vertically oblong position of the camera, with illumination through prisms, whereby the detection of visual axis is rendered possible in either position of the camera.
It is now assumed, as shown in FIG. 27, that two light-emitting elements (IRED) 201i, 201j for illuminating the eyeball of the observer are positioned symmetrically, in the horizontal position, with respect to a vertical plane containing the optical axis of the view finder system, when the camera 220 is in the normal position.
In such normal position of the camera 220, the corneal reflected images Pi, Pj formed by the illumination of the eyeball 15 of the observer by the IRED's 201i, 201j are focused on an image sensor provided in the camera 220, so that said two corneal reflected images can both be easily detected.
FIG. 28 is a schematic view showing the relationship between the two corneal reflected images Pi, Pj and the eyeball, wherein shown also are an eyelid 222 and eyelashes 223.
However, let us consider a situation shown in FIG. 29, in which the camera is held in a vertically oblong position, with the shutter releasing button 241 at the top. In such situation, as shown in FIG. 30, the two corneal reflected images Pi, Pj are aligned perpendicularly to the eyelid 222, so that a reflected image Pj is often eclipsed by the eyelid 222 and eyelashes 223 of the observer. Particularly under outdoor daylight, the eyelid is somewhat closed because of the high illumination intensity, so that the probability of eclipse of one of the corneal reflected images becomes extremely high. On the other hand, if the camera is in the vertically oblong position, with the shutter releasing button 241 closer to the ground, the other reflected image Pi tends to be eclipsed.
Therefore, in the above-explained conventional device in consideration of the vertical camera position, the position of illumination is so switched that two corneal reflected images are formed parallel to the eyelid, in the vertical or horizontal camera position.
When the observer supports the camera in standing position, satisfactory reflected images Pn, Pk can be obtained as shown in FIG. 33 when the shutter releasing button 241 is positioned closer to the ground. On the other hand, in the normal camera position or in the vertical camera position with the shutter releasing button close to the top, the illumination is made from the side of the upper eyelid of the observer, so that the two corneal reflected images are often eclipsed by the eyelid 222 or the eyelashes 223 as shown in FIGS. 31 or 32, whereby the detection of visual axis becomes difficult.
Also the present applicant already disclosed, in the Japanese Patent Application Laid-open No. 4-138432, an optical equipment with visual axis detecting means provided with means for discriminating whether the observer looking into the view finder wears spectacles, from the ghost of the eyeball illuminating light, reflected by the spectacles.
However, if an observer not wearing the spectacles is positioned close to the view finder, there will result strong reflected light from the eyelid or the eyelashes, and such reflected light may be recognized as ghost and the observer may be misidentified as wearing the spectacles. As a result, an observer without spectacles may be given illumination designed for the observer with spectacles, so that the precise visual axis detection may become impossible.
Also if an observer wearing the spectacles is positioned close to the view finder, the light reflected by the spectacles does not enter the visual axis detecting optical system, so that the ghost is not generated and the observer may be misidentified as not wearing the spectacles. As a result, the observer with the spectacles is given the illumination designed for the observer without the spectacles, whereby the visual axis detection may become impossible.